The present invention relates to a laser printer for performing printing at high speed and with a high picture quality and to a light source suitable for use in the laser printer.
It has been reported that variation of the shape of printing dots is effective for printing in a laser printer at high speed and with a high precision. That is, the number of scanning lines must be increased to achieve high precision. This means that a longer scanning time is inevitably required. Therefore, it has been proposed that, if the shape of the printing dots is varied, the time required for the scanning can be reduced. Such technology is disclosed, for example, in A. Arimoto et. al., MOC' 95 HIROSIMA previous report 300P-303P (Akira Arimoto et. al., Hitachi Research Laboratory, Hitachi, Ltd. "A Resolution Enhancement Printing with Variable Spot Size Laser"). This system employs the following technology. In a part of a stripe region comprising a light emission region of a semiconductor laser device operating as a light source, a modulation region is provided where current injection is performed to divide the region into two parallel stripes. When the current injection in the two stripes is modulated, a lens capable of being electrically controlled is formed. The spot diameter of light emission of this semiconductor laser device can be varied by this lens effect. The shape of the printing dots is varied using such a semiconductor laser device.